This application is based on Japanese Patent Application No. 2001-183230 filed on Jun. 18, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of estimating inertia moment or load of an internal combustion engine (engine), and a method of and apparatus for controlling the engine.
2. Description of Related Art
An engine control system controls fuel amount and ignition timing in order to operate the engine in best performance. In such an engine control system, fuel amount and ignition timing are controlled according to load of the engine so as to maximize output, improve fuel economy, reduce emission and the like. Therefore it is important to determine engine load in order to keep the engine in best performance. Engine load can be obtained based on a detected intake air amount, a detected opening degree of a throttle valve, a detected intake pressure and the like. In case of detecting such engine operating conditions, the system needs several sensors.
On the other hand, engine load can be estimated based on rotating engine speed. For instance, engine load can be estimated based on an engine speed fluctuation. The engine speed fluctuation can be obtained by monitoring a cyclic engine speed fluctuation At around a compressing top dead center of the engine as shown in FIG. 9. In FIG. 9, the engine speed fluctuation xcex94t is determined by detecting a maximum engine speed and a minimum engine speed during a combustion cycle of the engine. In FIG. 9, IN indicates an intake stroke, and EX indicates an exhaust stroke. The engine speed fluctuation xcex94t is substantially proportional to the engine load as shown in FIG. 10.
However, the relationships between the engine speed fluctuation and the engine load may vary in accordance with inertia moment which is rotational inertia moment on a crankshaft of the engine. In FIG. 10, lines A, B, and C indicate relationships between the engine speed fluctuation and the load under different inertia moments. Magnitudes of the inertia moments are as follows, A less than B less than C. Therefore, in order to estimate the engine load, it is necessary to obtain a parameter indicative of the inertia moment of the engine.
However, it is difficult to determine the inertia moment of the engine, because engine equipments can be changed. For example, in a multi-purpose engine, a purchaser of the engine will combine the engine with several equipments, and a user may replace the equipment. Therefore, it is difficult to determine the inertia moment of the engine at the time of manufacturing and shipping the engine. It is also difficult to adjust the inertia moment of the engine after combining the equipment on the engine, because such adjusting process will be complex and the user has to spend time.
Such a disadvantage may arise when estimating conditions of the engine that is affected by the inertia moment of the engine besides estimating the engine load as described above.
It is an object of the present invention, to provide a method that is capable of estimating inertia moment of an engine accurately.
It is another object of the present invention, to provide a method that is capable of estimating engine load accurately based on an estimated inertia moment of the engine directly or indirectly.
It is a still another object of the present invention, to provide a method of and apparatus for controlling an engine based on an estimated engine load.
According to an embodiment of the present invention, an inertia-related engine speed characteristic is obtained/measured when the engine is rotated without ignition. Therefore, the engine speed fluctuation reflects the inertia moment. As a result, the inertia-related engine speed characteristic is indicative of an inertia moment of the engine. The engine speed characteristic may be an engine speed fluctuation at a predetermined period or a predetermined stroke of the engine.
According to an embodiment of the present invention, an inertia-related engine speed fluctuation is obtained when the engine is rotated without ignition. The inertia-related engine speed fluctuation is indicative of an inertia moment of rotation of the engine. Therefore it is possible to control the engine in accordance with the inertia moment. The embodiment is based on knowledge that a fluctuation of the engine speed is increased around a compression top dead center of the engine when the engine is rotated without ignition and the fluctuation has a correlation to an inertia moment of the engine. In the invention, the inertia moment is estimated by using the correlation. Therefore it is possible to achieve the inertia moment without additional devices.
The estimated inertia moment can be used for several purposes that are influenced by the inertia moment. For example, the inertia moment can be used for estimating an engine load. But, the inertia moment can be indicated by another parameter such as the inertia-related engine speed fluctuation.
The engine load can be estimated accurately, because an influence of the inertia moment can be compensated. For example, the inertia moment can be reflected directly or indirectly on the estimating process. In case of above, it is possible to estimate the engine load accurately even if the equipment attached on the engine is not identified.
The estimated engine load can be used for controlling the engine. It is possible to achieve an adequate engine control in accordance with the engine load.
The engine speed fluctuation obtaining means may be a means for computing the engine speed fluctuation. For example, an engine speed fluctuation can be represented by a fluctuation of rotation angle within a predetermined time period, or, contrarily, a fluctuation of time periods for rotating a predetermined angle. The fluctuation of rotation angle can be obtained as a fluctuation of number of detected pulse signals. The fluctuation of time periods can be obtained as a fluctuation of number of clock pulses. The engine speed fluctuation obtaining means obtains the fluctuation within one cycle of the engine rotation. More specifically, at least a fluctuation between before and after a compression top dead center is obtained.
The inertia-related engine speed fluctuation and the load-related engine speed fluctuation are both the engine speed fluctuation detected by the means, and are characterized by periods for measuring the fluctuations.
For example, the inertia-related engine speed fluctuation is measured around the compression top dead center because the engine speed shows relatively large fluctuation. But the measuring period is determined to obtain a sufficient correlation between the fluctuation and the inertia moment. For example, a leading part of a momentary fall of the engine speed at the compression top dead center can be used for measuring the fluctuation. A trailing part of the momentary fall of the engine speed at the compression top dead center can be also used for measuring the fluctuation. In FIGS. 1 and 2, the momentary fall of the engine speed is illustrated, and exemplifies the case of using the trailing part of the momentary fall.
On the other hand, in case of obtaining the load-related engine speed fluctuation, the period for measuring is not limited around the compression top dead center of the engine. For example, the load-related engine speed fluctuation can be obtained based on a maximum and minimum engine speed in one cycle of the engine as shown in FIG. 9. Further, a period between a compression stroke and a combustion stroke or periods on both ends of the combustion stroke may be used for measuring the load-related engine speed fluctuation.